Bleeding brakes.....

[LeDevil]

I replaced my Master cylinder today here's the steps I took what did I do wrong?
I bench bleed the M/C as instructions said to and like I have many times before
I then bolted it to my brake booster
Hooked up the front line then the rear
had my fiancee pump the pedal until it was hard
I would open the back passenger bleeder valve until she said it hit the floor.
Told her no matter what not to lift her foot she did so.
I then closed the bleeder valve and repeated this until there was no air and the pedal was hard.
While bleeding I made sure there was always Brake fluid in the reservoir.

Well now when I have the truck running I push the brake it gos all the way to the floor and my Dummy Brake light comes on and the trucks slowly roll/lunges. So please tell me what I did wrong?
Thanks LeDevil

[MotorSeven]

Sounds like you may be openng the bleeder too long or too much. It lets air back in. Try it again & just barely crack the valves then close. LR, RR, LF then RF.

RD

[Bus Ted Knuckle]

did you reset the prop valve?

[LeDevil]

I didn't reset the Proportioning Valve how do I do that?

[cdowns]

Originally Posted by LeDevil

I didn't reset the Proportioning Valve how do I do that?

excellent info in the factory service manual how to bleed brakes and set the combination vvalve

[LeDevil]

I found the way to reset the valve while checking that I checked the brakes and I have no pressure build up what so ever even after pumping the pedal. The pedal go's straight to the floor and the Brake light comes on. I checked the check valve it's good, booster is good. Any ideas and I don't have any leaks any where. I've even used a pressure bleeder and still nothing. I am stumped!

[Stock72c10]

When I bleed mine I put a small piece of tubing on the bleeder (about 10-12 inches long) and insert it into a clear plastic cup that is about 1/4 full of brake fluid. Keep the end of the tube submerged in the brake fluid and unscrew the bleeder valve and have someone pump the brake pedal. When you don't see any more bubbles, close the bleeder valve back up before removing the tube from the cup of fluid, this will keep them from pulling air back into the wheel cylinder. Hope that makes sense.

[68gmsee]

You may have a defective master cylinder.

I went through 2 of them from local auto parts a few years ago before I decided to go to another parts store and get a different brand. Evidently they had a run of bad seals.

Another vehicle I did, I bled and bled (almost one large can of fluid) before I got rid of pockets of air trapped in the lines. I used clear plastic tubing and drained into glass container so I could see the fluid. In this last case, it didn't go all the way down. It was spongy.

[LeDevil]

Ok 3 M/C's later and the brakes are finally bleed I took it to the shop just to make sure and they said it was all good. But a problem still persists truck still lunges sometimes not as much but some times. I followed all the checks on this page and everything passed http://www.classicperform.com/TechBo...t.htm#testprop Could it be after I have the brakes pressed there might be a slight leak some where that I am not finding? I honestly can't find ANY brake fluid any where other then in the M/C the wheel cylinders seem to be solid? Any other Ideas?


EDIT: Thank you for all the previous help guys

[cparman]

Ok here is my 2 cents worth. You have worked your butt off trying to get a " pedal " on your truck. On your next day off, I want you to jack your truck up, and take the wheels off. One at a time I want you to open the bleeder screws. Starting at the right rear. Open the R.R. and look carefully to see fluid run from the bleeder. L.R. is next, and then go to the R.F. ETC. I cannot help but believe that you have air in the system. Sometimes at my shop, my young guys will get in a hurry, and not be able to get a " pedal ". The old farts will " SLOWLY BUT SURELY " gravity bleed " an old cars system, and like magic the pedal will be as it should be. Be sure to leave the truck alone over night, and then gravity bleed the system. The brake fluid could be full of air bubbles from all of the pumping of the brake pedal. I would have a hard time believing that you have gotten 3 bad master cylinders. DO NOT GIVE UP YOU CAN DO IT!!!

[Brad]

Just to clarify, wouldn't he need to start with the cyl farthest from the mc and work his way to closest? Wouldn't he start with ds rear, ps rear, then ps front, and finally ds front? He could also do ps front, ds front, then ds rear, ps rear since the front and rear are on two separate lines unlike the old 1 cyl master cylinder.

[LeDevil]

I was always told to start with the Passenger rear (farthest from the M/C), then the driver side rear, then the passenger front, then the driver front. But we'll see if the gravity bleeding works tomorrow when I got out check it tomorrow

[Brad]

Maybe I'm on something, but I couldna sworn that the ds rear is farthest away from the mc since the line goes over to the ps side up front across the crossmember and then back over on the rearend to the ds.

[kcjones]

Brad, you're right. Although the PS rear is geographically further, line distance wise, the DS rear is further. The line goes down from the m/c, across the cross member, along the PS frame rail, to the PS side of the rear end housing. The line from that junction is longer to the DS rear wheel cyl than it is to the PS, so yes: the DS rear is technically a longer brake-line distance from the M/C.

Bleed them like this: DS rear, PS rear, PS front, DS front. It is possible that since you're doing the PS first, you're getting air stuck in the lines on or near the rear end housing.